Mulch films have been used in agriculture for many years to confine chemical treatment agents, such as soil fumigants, to the areas where they are applied. The materials commonly used in the manufacture of such mulch films are polyethylene materials. The polyethylene mulch films are well suited for such use due to their ability to resist puncturing and tear propagation. However, one drawback of such films is that they allow the escape of volatile gaseous soil fumigation compounds such as, for example, methyl bromide, chloropicrin, methyl iodide, dimethyl disulfide, and telone, among others.
Methyl bromide (MeBr) is an odorless, colorless gas that has been used by the agricultural industry as an agricultural soil and structural fumigant to control a wide variety of weeds and pests. However, MeBr is also classified as a Class 1 ozone-depleting substance, and the agricultural industry has therefore sought to develop barrier mulch films that allow for lower MeBr usage rates per acre by more effectively confining the fumigant during the course of treatment.
For example, PCT application WO84/00553 discloses an olefin polymer barrier film that incorporates one or more fatty acid derivative compounds to reduce the permeability of gaseous chemical treatments, such as MeBr and chloropicrin, through the film. Preferred permeability reducing derivative compounds are monoamides, bisamides, amines and esters of polyhydric alcohols. According to the disclosure, MeBr permeability is reduced by more than 10% by the incorporation of the fatty acid derivatives into the film materials.
U.S. Pat. No. 4,538,531 to Wong discloses a method of confining soil fumigation compounds to areas of treated soil by utilizing an olefin polymer film which similarly incorporates the fatty acid derivative compounds disclosed in WO84/00553.
Japanese Publication No. JP 10272715 discloses a coating composition for forming a methyl bromide barrier film which comprises an organic compound having a primary or secondary amino group in the molecule and an organic metal compound.
In recent years, the mulch barrier film market has been dominated by metallized polyethylene films. One such film is commercially available from Canslit, Inc., Montreal, Canada. With metallized films, a thin metal layer of, for example, aluminum, is deposited on the film in a vacuum chamber. Such films are primarily polyolefin based and consequently have excellent resistance to tearing, but their barrier properties are much lower compared to a mulch film containing a nylon barrier layer. Also, the metal layer can disintegrate or dissolve under a variety of soil and weather conditions. Once this happens, the barrier properties of the metallized film are lost.
Another type of commercially available mulch barrier film is a virtually impermeable film (VIF). Such VIF's typically contain a nylon layer, which is known to have excellent barrier properties. Although commercial VIF's have excellent barrier properties and are not susceptible to barrier loss by weather or soil conditions, they are not as resistant to puncturing and tear propagation as polyethylene mulch films. As a result, nylon multilayer mulch barrier films have only had limited use in the agricultural industry despite nylon's excellent barrier properties.
There is still a need for an agricultural mulch barrier film that can meet the needs of the industry. That is, a mulch barrier film that (1) has excellent barrier properties that are resistant to barrier loss from external conditions, (2) has excellent tear strength, and (3) is economical to produce.